During surgical harvesting of vessels, a target vessel is exposed, tributaries are ligated and transected, and the vessel is harvested. In order to view the vessel, a cannula housing an endoscope is inserted into a surgical cavity to visualize the adventitial layer of a target vessel. The vessel is tracked by advancing the cannula along the path of the vessel while bluntly dissecting the cavity as the cannula is advanced. Upon viewing a side branch or tributary of the vessel, a surgical tool is inserted into the surgical cavity to cauterize and sever the side branch. The endoscope remains in the surgical cavity during this process to allow the surgeon to view the procedure, and the size of the cavity is maintained using insufflating gas. Using different tools simultaneously in a surgical cavity is difficult due to the small size of the surgical cavity. Additionally, within the surgical cavity, the surrounding tissue typically collapses upon the cannula and surgical tools, increasing the difficulty of the operation, if performed without insufflation. However, maintaining the surgical cavity open using insufflation with gas under pressure then also requires sliding gas-tight seals for each endoscopic instrument that is inserted into the surgical cavity.
Current systems commonly employ a balloon coupled to the cannula for intermittent inflation and deflation to enlarge the surgical cavity as the cannula is advanced. However, use of a balloon to enlarge surgical cavities has the disadvantage that multiple balloon inflation and deflation tires the surgeon's hands, and makes it difficult to retain the precise hand control needed to perform the surgical procedure. Also, manufacture of a balloon cannula requires manual mounting of the balloon in a tedious process that adds expense to the device. Additionally, balloons have a potential for rupture during use and thereby disrupt the surgical procedure. Thus, a device is needed which retains the endoscopic vessel tracking ability of current systems, while also enlarging the surgical cavity without the disadvantages of balloon systems.